Water Pollution Continuous Monitoring Technology in Japan
Overview of Water Pollution Monitoring Conducted by Local Governments in Japan
Factories and establishments that discharge more than 400 cubic meters of waste water a day into public water areas are obligated to automatically monitor organic pollutants in the waste water. Data from these automatic monitoring systems are transmitted to the central control station through the telemeter system for evaluating compliance with regulations on total pollution load of COD.
In Osaka City Government, 8 factories and 12 sewage treatment plants have been required to install automatic monitoring systems. Measurement data from these factories and plants are sent to the central station for evaluation.
In Osaka Prefectural Government, pollution source telemeter systems have already been installed at 44 factories and establishments discharging more than 3,000 cubic meters of waste water per day. This allows the prefecture to monitor 80% of its industrial pollution load.
(1) Continuous monitoring of pollutant load
The continuous monitoring system installed at each factory and sewage treatment plant must be able to automatically measure water quality and flow rate and calculate each day's pollutant load. Automatic analyzers are chosen, located and installed according to the condition of the waste water system in each factory or business establishment. All industrial waste water must be sampled and analyzed, but only rain water, indirect cooling water or domestic waste water are excluded.
(2) A typical monitoring system
A typical monitoring system includes a flow meter, an automatic analyzer (Ultraviolet (UV) absorption meter), a load processor, a telemeter system, data communication equipment and a data processor.
Flow meter:
A model appropriate for the drainage channel and other drainage conditions should be selected. Electromagnetic flow meter may be necessary depending on the condition of the factory or establishment.
UV absorption meter:
UV absorption is promptly measured in continuously supplied samples to detect real-time concentration of organic pollutants. UV absorption by muddy substances is corrected by visible absorption.
Load processor:
The signals output from flow meter and UV absorption meter are sent to the load processor for calculation of pollution load and average value for water pollution. The load processor transmits these daily data to the telemeter system by digital signal.
(3) Data processing method
The momentary UV absorption level measured by the UV absorption meter is converted into COD-based water quality, using a preset coefficient at 1-minute intervals. The momentary pollutant load is then calculated using the converted COD-based water quality level and the momentary flow rate. The sum of momentary pollutant loads during an hour is output as the hourly pollutant load. The hourly average water pollution is converted into COD value by dividing the hourly pollutant load by the hourly flow volume.
[Input signal]
[Output signal]
(4) Data transmission and data retrieval
The host computer at the central station is transmitted stored data from each factory's pollution source telemeter system once a night, through the communication line by telephone. The host computer also is transmitted data every hour from the telemeter system installed at each sewage treatment plant.
[Transmission method]
(5) Telemeter central station
A telemeter central station consists of a network terminal connected to the communication line by telephone, data communication equipment, a network controller for the communication line, an automatic dialing device, and a standard clock using crystal oscillation.
(6) Data processor
A data processor is used to process data collected from factories or establishments.
The fig.3.2.3 below shows the structure of a typical pollution-source monitoring system.
Sewage treatment plant
Monitoring station
Ultraviolet(UV) analyzer
Ultraviolet(UV) analyzer
Load amount calculator
Telemeter unit of monitoring station
